Absence of scalenus anterior muscle

A rare anomaly of the scalenus muscles is described. In this case, the right scalenus anterior muscle was absent. As a substitute for this muscle, some aberrant muscle slips arose from the lower vertebrae and descended in front of the ventral rami of the lower cervical nerves. These aberrant slips then ran between the ventral rami of the the eighth cervical and first thoracic nerves, and were fused with the right scalenus medius muscle. Thus, the subclavian artery and vein ran in front of the aberrant slips, together with the ventral ramus of the first thoracic nerve. The aberrant muscle slips issued 2 accessory bundles. One bundle ran between the ventral rami of the fourth and fifth cervical nerves and was fused with the scalenus medius muscle; the other bundle ran between the ventral rami of the fifth and sixth cervical nerves and was fused with the scalenus medius muscle.     

Variations of the ventral rami of the brachial plexus.

We studied the variations in the ventral rami of 152 brachial plexuses in 77 Korean adults. Brachial plexus were composed mostly of the fifth, sixth, seventh and eighth cervical nerves and the first thoracic nerve (77.0%). In 21.7% of the cases examined, the fourth, fifth, sixth, seventh and eighth cervical and the first thoracic nerves contributed to the plexus. A plexus composed of the fourth, fifth, sixth, seventh and eighth cervical and the first and second thoracic nerves, and a plexus composed of the fifth, sixth, seventh eighth cervical nerves were also observed. The plexuses were classified into three groups according to cephalic limitation, and the plexus of group 2 in which the whole fifth cervical nerve enters the plexus, were observed the most frequent. The average diameter of the sixth and the seventh cervical ventral rami of the plexus was greatest and that of the fifth cervical was smallest. The largest nerve entering the plexus was the sixth or the seventh cervical nerve in about 79% of cases. The dorsal scapular nerve originated from the fifth cervical ventral ramus in 110 cases (75.8%). The long thoracic nerve was formed by joining of roots from the fifth, sixth, and seventh cervical nerves in 76.0% of cases. Also, a branch to the phrenic nerve, the suprascapular nerve, a nerve to the pectoralis major muscle and a nerve to the subscapular muscle arising from the ventral rami of the plexus were observed.     

Spatial relationships between the morphologies and innervations of the scalene and anterior vertebral muscles

The prevertebral muscles are innervated by the cervical ventral rami. However, little information is available on the spatial relationships between the muscles and the supplying branches. This gross anatomical study investigated the prevertebral muscles and the nerves in 26 cadavers to elucidate their spatial interrelationships and the nerve pathways to each muscle. These muscles were characterized by the variations in the vertebral attachments. The scalenus medius was divisible into the dorsal and ventral parts. The scaleni anterior and medius attached to both the anterior and posterior tubercles of the cervical transverse processes. The oblique fibers arising from the transverse processes joined the vertical part of the longus colli. The rectus capitis anterior, the longus capitis and the scalene anterior and minimus were innervated by the ventromedial branches of the cervical ventral rami, and the branches passed between the origins of the proximal muscles to supply the longus colli. The rectus capitis lateralis and the scalenus medius were innervated by their dorsolateral branches, and the branches pierced the medius to the scalenus posterior. The roots of the brachial plexus passed between the scalenus anterior and the ventral part of the medius. The penetrations by the upper roots and the interconnecting fibers passing between the roots were found in the muscle bundles arising from the fourth or fifth cervical vertebrae. Their anomalies are the possible causes of the cervical-brachial disorders, and the knowledge of the innervation and the variations in this study seems to be useful for surgical and non-surgical treatments.     

On the rami intermedii of the spinal nerves and their equivalent offshoots

Summary Distribution patterns of the nerves of supply to the intertransversarii posteriores cervicis, levatores costarum breves and intertransversarii laterales lumborum were carefully studied in nine body-halves of male human cadavers. Any of these muscles lie wegded in between the commencements of the dorsal and ventral primary rami of the spinal nerves. In the great majority of the cases the levatores costarum breves derived their nerve supply in the upper segments from both primary rami of the corresponding spinal nerves and in the lowest segments as the rami intermedii from the bifurcation of each spinal nerve into its primary rami. Both patterns of the nerve supply to the levatores costarum breves were turned into one another in the intervening segments. The intertransversarii posteriores cervicis of similar location to the levatores costarum breves in the thoracic region were regarded as the upper serial homologues of these muscles, because they were supplied by both primary rami of the spinal nerves, similarly the intertransversarii laterales lumborum, principally supplied by the rami intermedii of the spinal nerves, as the lower serial homologues of the same muscles.In view of location as well as mode of innervation it was proposed that the intertransversarii posteriores cervicis, levatores costarum breves and intertransversarii laterales lumborum should be grouped into the musculi intervertebrales laterales (abbrev. l) as the serially homologous muscles deriving innervation of an ambiguous character from both primary rami of the spinal nerves and therefore as the third muscle system more or less distinct from the musculi trunci dorsales (abbrev. D, Nishi) and ventrales (abbrev. V, Nishi) which are supplied alternatively by either of the primary rami of the spinal nerves.     

The medial branch of the lateral branch of the posterior ramus of the spinal nerve

In the needle insertion of epidural anesthesia with the paramedian approach, the needle can pass through the longissimus muscle in the dorsum of the patients. When the needle touches a nerve in the muscles, the patients may experience pain in the back. Obviously, the needle should avoid the nerve tract. To provide better anesthetic service, analysis of the structure and where the concerned nerves lie in that region is inevitable. Material and method: We studied five cadavers in this study. Two cadavers were fixed with Thiel’s method. With these cadavers, we studied the nerve running of the posterior rami of the spinal nerve from the nerve root to the distal portion. Three of them were used for the study of transparent specimen, with which we studied the course and size of the nerve inside the longissimus muscle. Results: We observed there were three branches at the stem of the posterior rami of the spinal nerves between the body segment T3 and L5, i.e. medial branch, medial branch of the lateral branch and lateral branch of the lateral branch. The medial branch of the lateral branch supplied to the longissimus muscle. With the transparent specimen, we found that there were different nerve layouts between the upper thoracic, lower thoracic, upper lumbar, and lower lumbar segments in the medial branch of the lateral branch in the longissimus muscle. In the lower thoracic and upper lumbar segments, the medial branch of the lateral branch of the upper lumbar segments produced layers nerve network in the longissimus muscle. L1 and L2 nerves were large in size in the muscle. Conclusion: In the upper lumbar segments the medial branch of the lateral branch of the posterior rami of the spinal nerve produced dense network in the longissimus muscle, where the epidural needle has high possibility to touch the nerve. Anesthetists have to consider the existence of the medial branch of the lateral branch of the posterior rami of the spinal nerve when they insert the needle in the paramedical approach to the spinal column.     

Nerves and nerve plexuses of the human vertebral column

The origin, distribution, and termination pattern of nerves supplying the vertebral column and its associated structures have been studied in the human fetus by means of an acetylcholinesterase whole-mount method. The vertebral column is surrounded by ventral and dorsal nerve plexuses which are interconnected. The ventral nerve plexus consists of the nerve plexus associated with the anterior longitudinal ligament. This longitudinally oriented nerve plexus has a bilateral supply from many small branches of the sympathetic trunk, rami communicantes, and perivascular nerve plexuses of segmental arteries. In the thoracic region, the ventral nerve plexus also is connected to the nerve plexuses of costovertebral joints. The dorsal nerve plexus is made up of the nerve plexus associated with the posterior longitudinal ligament. This nerve plexus is more irregular and receives contributions only from the sinu-vertebral nerves. The sinu-vertebral nerves originate from the rami communicantes and, in the cervical region, also from the nerve plexus of the vertebral artery. Thick and thin sinu-vertebral nerves are found. Most frequently three types of thick sinu-vertebral nerves are observed, i.e., ascending, descending, or dichotomizing ones. Finally, the distribution of the branches of the ventral and dorsal nerve plexuses and of the sinu-vertebral nerves is described.     

Localization of motoneurons that extend axons through the ventral rami of cervical nerves to innervate the trapezius muscle: a study using fluorescent dyes and 3D reconstruction method

It has been suggested that in addition to motor axons, which extend directly into the spinal accessory nerve (SAN), ventral rami-associated motor fibers of cervical nerves also innervate the trapezius muscle. Using fluorescent dye labeling and 3D reconstruction in adult rats, this study clarifies the localization of motoneurons, which extend axons either directly through the SAN or through the ventral rami of cervical nerves to innervate the trapezius. DiI or DiI and DiO were used to label the ventral rami of cervical nerves entering the SAN, as well as branches of the SAN. We show that motoneurons whose axons pass through the ventral rami of cervical nerves and then enter the SAN, and those extending axons directly through the SAN are distributed within the same area. The neurons that extend axons through the SAN had a greater diameter than those axons that pass through the cervical nerves en route to the trapezius muscle. In addition, the axons that ultimately extend through the SAN exit the spinal cord dorsolaterally, while those that pass through the cervical nerves extend out the spinal cord through the ventral roots. We presume that the neurons that extend axons through the SAN are mainly alpha-motoneurons and that those projecting axons through the cervical nerves to the trapezius are mainly gamma-motoneurons. Taken together, these results could explain why patients in whom the SAN was used to treat brachial plexus injury retain some control of the trapezius muscle.     

Novel concept for the epaxial/hypaxial boundary based on neuronal development

Trunk muscles in vertebrates are classified as either dorsal epaxial or ventral hypaxial muscles. Epaxial and hypaxial muscles are defined as muscles innervated by the dorsal and ventral rami of spinal nerves, respectively. Each cluster of spinal motor neurons passing through dorsal rami innervates epaxial muscles, whereas clusters traveling on the ventral rami innervate hypaxial muscles. Herein, we show that some motor neurons exhibiting molecular profiles for epaxial muscles follow a path in the ventral rami. Dorsal deep-shoulder muscles and some body wall muscles are defined as hypaxial due to innervation via the ventral rami, but a part of these ventral rami has the molecular profile of motor neurons that innervate epaxial muscles. Thus, the epaxial and hypaxial boundary cannot be determined simply by the ramification pattern of spinal nerves. We propose that, although muscle innervation occurs via the ventral rami, dorsal deep-shoulder muscles and some body wall muscles represent an intermediate group that lies between epaxial and hypaxial muscles.     

Fiber arrangements of cutaneous and muscular rami in cervical nerves of the rat--regarding conception of the spinal nerve stratum-structure

Fluorescence tracers DiO and DiI were applied to compare fiber arrangements of cutaneous and muscular rami in the proximal region of anterior and posterior branches of cervical nerves. Results show that a ventrodorsal relationship of cervical nerves is observed in gross level; however, fiber arrangements of cutaneous and muscular rami differ in anterior branches according to distance from the anterior root and dorsal root ganglia. That is, the fibers have a scattering course (no ventrodorsal relationship) in distal regions. Moreover, just before entering anterior roots, the motor fibers of muscular ramus run through the ventral part and sensory fibers of muscles and fibers of cutaneous ramus run through the dorsal part and intersect with motor fibers of the posterior muscular ramus. In contrast with the anterior one, in posterior branches of cervical nerves, cutaneous and muscular rami fibers are very regularly arranged in the distal and proximal region. Based on these results, the ventrodorsal relationship of fiber arrangements could exist in posterior branches and proximal region of anterior branches. Present results differ with those of the spinal nerve stratum-structure; therefore, they are insufficient to elucidate the relationship of peripheral nerves by conception of spinal nerve stratum-structure.     

Bilateral subclavian arteries passing in front of the scalenus anterior muscles

Herein, we present a very rare case of bilateral subclavian arteries passing in front of the scalenus anterior muscles in a cadaver. This abnormality was observed in a 73-year-old Japanese male cadaver during a dissection session for students in 2004 at Osaka Dental University. The bilateral scalenus anterior muscle originated from the anterior tubercle of the transverse processes of the fifth and sixth cervical vertebrae and inserted into the scalene tubercle of the first ribs. The right scalenus minimus muscle was observed, but no left scalenus minimus muscle was observed. The aortic arch was a type A according to Adachi's classification. The origin of the internal thoracic artery was distal to that of the thyrocervical trunk. The bilateral brachial plexuses was formed by the union of the ventral rami from the fifth cervical to the first thoracic nerves and passed between the scalenus anterior and the scalenus medius muscles. To our knowledge, such a case has not been reported previously.     

The long thoracic nerve: Its origin,branches, and relationship to the middle scalene muscle

Anatomical knowledge regarding the long thoracic nerve (LTN) is important during surgical procedures considering that dysfunction of this nerve results in clinical problems. The purpose of this study was to explore the anatomy of the LTN, its origin, configuration, branching pattern, and relationship to the middle scalene muscle (MSM). The course of the LTN was investigated in 12 embalmed cadavers (21 sides). We defined four different types for this nerve according to the origins of its roots. The most common formation of the LTN was the contribution of three branches that originated from the fifth, sixth, and seventh cervical ventral roots. C5 and C6 components or upper portion of the LTN roots lay primarily between the middle and posterior scalene muscles, sometimes passed through the MSM, and less frequently coursed over the MSM. C7 contributions to the LTN were always located anterior to the MSM. Contributions from C8 were also found over the MSM. The median number of branches arising directly from the cervical roots and branches arising from the main trunk of the nerve were 3 and 7, respectively. Along its course, the median number of branches to the serratus anterior was 10. Clin. Anat. 22:476–480, 2009. © 2009 Wiley‐Liss, Inc.     

Anatomical variations of the upper thoracic sympathetic chain

The aim is to clearly delineate the upper thoracic sympathetic chains and neural connections between the chains and ventral rami of the thoracic nerves, and to provide an anatomical foundation for successful upper thoracic sympathicotomy for treating upper essential hyperhidrosis. The upper thoracic sympathetic chains, upper five intercostal nerves, and neural connections between them in 50 halves of 25 adult cadavers have been dissected, measured, and mapped. The stellate ganglion had an incidence of 80%. The second to the fourth thoracic sympathetic ganglia were commonly located in the corresponding intercostal spaces with the presence of 92%, 68%, and 50%, respectively. The incidence of the first and second intercostal rami was 40% and 6%, and that of the ascending or descending rami from the second, third and fourth ganglia was 54%, 24%, and 14%, respectively. Additional rami communicantes joined the ventral ramus of the 1st thoracic nerve proximal to the point where the latter gave a branch to the brachial plexus. The farthest horizontal distance from the sympathetic chain to the junction between the additional rami communicantes and the second to the fourth intercostal nerves was 29.1 mm. Only 16% of cadavers had similar anatomy bilaterally. Anatomical variations of the upper thoracic sympathetic trunk in relation to intercostal nerves, which may be one of the causes resulting in surgical failures and recurrences, were striking. Attention should be given to such anatomical variations when planning thoracic sympathicotomy. Clin. Anat. 22:595–600, 2009. © 2009 Wiley‐Liss, Inc.     

Branches of the thoracic sympathetic trunk in the human fetus

Summary The segmental organization of the thoracic sympathetic trunk and all its ramifications was studied in 6 human fetuses (16–22 weeks) by means of the acetylcholinesterase in toto staining method. Each trunk was divided into 12 sympathetic segments. A segment is defined as that part of the sympathetic trunk which is connected via its rami communicates with one spinal nerve, without discriminating between grey and white rami. The diameter of the rami communicantes and their direction towards the spinal nerves are variable. The number of peripheral segmental ramifications of the trunk is much larger than assumed previously. Each thoracic sympathetic segment gives off at least 4–5 nerves. Three categories of nerves are discerned: (1) large splanchnic rootlets confined to the greater, lesser and least thoracic splanchnic nerves, (2) medium-sized splanchnic nerves directed towards thoracic viscera, some of which give off branches towards costovertebral joint plexuses and, described for the first time in man, (3) small nerves which ramify extensively and form nerve plexuses in the capsule of the costovertebral joints. The majority of the ramifications is formed by the nerves of the third category. The existence of Kuntz's nerve, connecting the 2nd intercostal nerve and 1st thoracic spinal nerve, is confirmed in four specimens. The nerve plexuses of the costovertebral joints receive a segmentally organized innervation: they receive their input from the neighbouring sympathetic segment and the one cranial to it.It is concluded that the thoracic sympathetic branches in man show a complex, segmentally organized pattern and may have a considerable component of somatosensory nerve fibers. The complex relationships must be taken into account in surgical sympathectomies.     

Morphological study, by teasing examination, of the communication from the musculocutaneous to median nerves

Nine specimens with communications from the musculocutaneous to the median nerves were investigated, by teasing examination, from their origins in the brachial plexus to their final destinations in nerve fibers. The nerve fibers of the communications were derived from the sixth and seventh cervical ventral rami of the spinal nerves. The distributions of the nerve fibers of the communications were divided into four types. In Type A, the nerve fibers reached the thenar muscles and the lateral digital nerves. In Type B, they reached the pronator teres or flexor carpi radialis muscles in addition to Type A. In Type C, they reached the anterior interosseous nerve area in addition to Type B. Finally in Type D, they also reached the distal muscle belly of the index of the flexor digitorum superficialis. It was revealed that there was a definite rule in the distribution of the nerve fibers in the communications from the musculocutaneous to median nerves. The area of the distributions was expanded in order from the thenar muscles to the flexor muscles of the forearm. The results in this study are useful for proper diagnosis and treatment of the peripheral nerve injuries involving the musculocutaneous and median nerves.     

A case of the scalenus anterior muscle passing behind the left subclavian artery

The scalenus anterior muscle was found to pass behind the left subclavian artery and the first thoracic nerve in a 95-year-old Japanese woman. The scalenus anterior muscle originates from the fifth and sixth cervical vertebrae and inserts on the first rib more dorsal than typical. It is innervated by the fifth and seventh cervical nerves. The muscle belly is thin. The scalenus minimus was not found. The left vertebral artery originates from the aortic arch and enters the transverse foramen of the fifth cervical vertebra. The primary vertebral artery arises from the costocervical artery. The internal thoracic artery originates from the subclavian artery more distally than typical. The axillary artery crosses the brachial plexus between the eighth cervical and first thoracic nerves. Because the first thoracic nerve joins the brachial plexus more distally than usual, the plexus has no typical inferior trunk. Comparative anatomy shows that the muscles, nerves and arteries of the lateral cervical region of the present case maintains primitive characteristics. From the functional viewpoint, the mechanical efficiency of the scalenus anterior muscle is probably lower than usual due to the lower point of origin and the dorsal shift of the insertion.     

Scalenus muscles in macaque monkeys

The attachment and innervation of the scalenus muscles in both sides of two Japanese monkeys and a rhesus monkey were observed to discuss their morphological significance while comparing their findings in humans. The scalenus ventralis muscle in macaques had almost the same attachments as the scalenus anterior muscle in humans and was innervated by the cervical nerve branches, which were lower in spinal segment than in humans and had a close relationship with the branches to the intertransversus ventralis muscles. Furthermore, the scalenus ventralis muscle was penetrated by the phrenic nerve in all cases observed. The posterior part of the scalenus muscle in macaques (the scalenus dorsalis muscle) was divided into short (the scalenus dorsalis brevis) and long (the scalenus dorsalis longus) parts according to their attachments. The former was attached to the transverse processes of the lowest two cervical vertebrae and the first rib, whereas the latter was attached to the 3rd-5th ribs. It is notable that the scalenus dorsalis muscles in macaques were innervated by branches from the long thoracic nerve in addition to direct branches from the cervical nerve roots. In addition, the scalenus dorsalis longus was supplied by twigs from the lateral cutaneous branches of the 2nd and 3rd intercostal nerves. This indicates that the scalenus dorsalis muscles contain a muscular component derived from the upper limb girdle musculature, unlike the human scalenus muscles, which have been considered to belong to the cervical trunk muscles.     

Anatomical Study of the Brachial Plexus in the Common Marmoset (Callithrix Jacchus)

To elucidate the forelimb phylogeny of primates, anatomical analysis of the brachial plexus in platyrrhines is beneficial. In the present study, six brachial plexuses and the surrounding arteries of four common marmosets were dissected. In five specimens, the brachial plexus consisted of five ventral rami from the fifth cervical nerve (C5) to the first thoracic nerve (T1). In one specimen, the ventral ramus of the fourth cervical nerve joined with the brachial plexus. In five specimens, the upper trunk was composed of C5 and the sixth cervical nerve (C6). In one specimen, the ventral division of C6 merged with the ventral branch of the middle trunk to constitute the lateral cord. The seventh cervical nerve constituted the middle trunk, and the eighth cervical nerve and T1 formed the lower trunk in all specimens. The lateral cord gave rise to the musculocutaneous nerve, and the remaining component merged with the medial cord. The confluence of the lateral and medial cords immediately bifurcated into the median and ulnar nerves. These branching patterns of the musculocutaneous, median, and ulnar nerves were consistent and similar to the human counterparts. In the dorsal division, the single posterior cord as observed in the human brachial plexus was not observed. The axillary artery did not pass between the medial and lateral roots of the median nerve, and the axillary artery bifurcated into the brachial artery and the superficial brachial artery. Anat Rec, 300:1299–1306, 2017. © 2017 Wiley Periodicals, Inc.     

Sexual dimorphism of the posterior cervical spine muscle attachments

Cervical spinal injury and neck pain are common disorders with wide physical implications. Neck pain and disability are reported to occur in females more often than in males, and chronic or persistent neck pain after whiplash is twice as common in females. Female athletes also sustain a higher percentage of concussions compared to male athletes. Still, while sexual differences in clinical presentation and outcome are well-established, the underlying etiology for the disparity remains less clear. It is well-established that the origin and insertion landmarks of posterior neck muscles are highly variable, but we do not know if these interindividual differences are associated with sex. Expanding our knowledge on sexual dimorphism in the anatomy of the cervical muscles is essential to our understanding of the possible biomechanical differences between the sexes and hence improves our understanding as to why females suffer from cervical pain more than males. It is also of paramount importance for accurate planning of posterior cervical spine surgery, which cuts through the posterior cervical musculature. Therefore, our main objective is to characterize the anatomy of posterior neck musculature and to explore possible sexual differences in the location of their attachment points. Meticulous posterior neck dissection was performed on 35 cadavers, 19 females, and 16 males. In each specimen, 8 muscle groups were examined bilaterally at 45 osseous anatomical landmarks. Muscles and their attachment sites were evaluated manually then photographed and recorded using Microscribe Digitizer technology built into 3D models. A comparison of attachment landmarks between males and females for each muscle was conducted. Out of the eight muscles that were measured, only two muscles demonstrated significant sex-related anatomical differences—Spinotranversales (splenius capitis and cervicis) and Multifidus. Male Spinotransversales muscle has more attachment points than female. It showed more cranial insertion points in the upper cervical attachments (superior nuchal line, C₁ posterior tubercle, and mastoid process) and more caudal insertion points in the spinous processes and transverse processes of the lower cervical and upper thoracic vertebrae. Thus, the male subjects in this study exhibited a greater coverage of the posterior neck both cranially and caudally. Female Multifidus has more attachment points on the spinous processes and articular processes at middle and lower cervical vertebrae and at the transverse processes of the upper thoracic vertebrae. All remaining muscles exhibited no sexual differences. Our findings highlight, for the first time, a sexual dimorphism in attachment points of posterior cervical musculature. It reinforces the notion that the female neck is not a scaled version of the male neck. These differences in muscle attachment could partially explain differences in muscle torque production and range of motion and thus biomechanical differences in cervical spine stabilization between sexes. It sheds a much-needed light on the reason for higher whiplash rates, concussion, and chronic cervical pain among females. Surgeons should take these sexual morphological differences into consideration when deliberating the best surgical approach for posterior cervical surgery.     

Danger of damaging the medial branches of the posterior rami of spinal nerves during a dorsomedian approach to the spine

Postoperative atrophy of the deep back muscles may be caused by denervation during a dorsomedian approach to the thoracolumbar spine; ensuing instability of the spine with poor clinical results, perhaps due to such muscle loss, has been observed in 11.7% of cases (Sihvonen et al., 1993, Spine 18:575--581). More specifically, this complication may be caused by damaging the medial branches of the posterior rami of the spinal nerves during lateral retraction of the muscles. To investigate the anatomic topography of the medial branches of the posterior rami of the spinal nerves, 18 carbol-formol-fixed specimens were dissected using an operation microscope; also, 3 fresh cadavers were cut in horizontal and vertical planes with a rotary cryotome to confirm the anatomic topography observed in the fixed specimens. In the thoracolumbar spine the medial branch of the posterior ramus of the spinal nerve is subject to ligamentous fixation by the strong fibers of the mammillo-accessory ligament, which extends between the mammillary process and accessory process infero lateral to the superior articular process. When the dorsomedian approach to the thoracolumbar spine is enlarged laterally to the articular processes by retracting the paraspinous muscles, the medial branches of the posterior rami of the spinal nerves are endangered. This may cause postoperative pain as well as dynamic instability beyond the corresponding segments. The results of our anatomic study suggest that the posterior surgical midline approach to the thoracolumbar spine should not be enlarged laterally to the articular processes to prevent injury to the medial branches of the posterior rami of the spinal nerves.     

Nerve contributions to the pelvic plexus and the umbilical cord

Serial sections of human embryos and fetuses reveal that the sacral nerves which contribute fibers to the pelvic plexus often have dorsal, ventral, and oblique communicating rami. The ventral rami resemble the white rami of upper thoracic nerves and some of their fibers pass close by or through the chain ganglia and into the pelvic plexus. The sizes of the ventral rami are often in inverse proportion to that of the pelvic splanchnic nerves. That is, when the pelvic splanchnic nerves are poorly developed, the ventral rami are large, and conversely, when the pelvic splanchnic nevers are well developed, these rami are small. The pelvic plexus was found to receive fibers from the sympathetic trunk and its ganglia in addition to those from the hypogastric plexus and the pelvic splanchnic nerves. Analysis of the observations made in this study together with a review of the literature in light of the present day classification of nerve fibers raises serious doubts concerning the limits set for the outflow of preganglionic nerve fibers from the spinal cord and the distribution of gray and white rami as described in recent textbooks in terms of their histological and physiological significance. Nerve fibers from the pelvic plexus can be traced along the walls of the bladder and the urachus and along the umbilical arteries into the umbilical cord. In embryos, only a few scattered nerve fibers were found distal to the umbilicus, but in fetuses at term, distinct nerve bundles were identified in the cord. These bundles sent branches to the walls of the umbilical arteries; other branches terminated as “end-nets” in Wharton's jelly. These nets appeared as fine fibers with nodular swellings at irregular intervals. Innervation of the umbilical arteries was richest within the first few inches of the cord. Beyond this region, the nerves rapidly decreased in number. “End-nets” were present as far as four inches from the umbilicus. Granular cells resembling Langerhans' cells were found in the cord. Often these cells were closely associated with fine nerve fibers.